1. Field of the invention
The present invention relates to a ball mill for grinding materials such as cement clinker and, more particularly, to a flow rate regulator to be used in combination with a partition diaphragm in the ball mill, the partition diaphragm being formed inside a body of the mill and having multi-grinding chambers.
2. Prior art
Generally, plural grinding chambers, i.e., multi-grinding chambers are provided in a ball mill for the purpose of improving productivity while reducing energy cost per material thereby improving the grinding efficiency as a whole, and in which a series of grinding processes are performed comprising the steps of primarily grinding a bulky material using a ball of large diameter (serving as grinding medium) in a primary grinding chamber; filtering the material ground to a certain grain size; feeding the filtered material to a secondary grinding chamber; and grinding the fed material finely.
For that purpose, it is an essential requirement to balance the level of material supplied in the primary grinding chamber with the level of material supplied in the secondary grinding chamber. It is often the case, however, that the amount of material fed from the primary grinding chamber to the secondary grinding chamber passing through the filtering slits exceeds the grinding capacity of the secondary grinding chamber, and that a number of relatively large size grains are mixed in the material and left in the material fed to the secondary grinding chamber and discharged therefrom as they are not ground further. This results in the application of a further load on the secondary grinding chamber. Such a disadvantage can be obviously recognized by checking the lowest level of the material presented in the vertical section of the first and second grinding chambers as shown in FIG. 5. That is, referring to FIG. 5, the level of the moving material immediately before the partition diaphragm of the primary grinding chamber is largely lowered, and as a result the grinding efficiency at this portion is also largely lowered. This negative influence is carried over to the next secondary grinding chamber, and such an unbalanced movement of the material will eventually bring about a decline in the grinding performance of the entire ball mill.
To regulate the balance between the two grinding chambers, first it is necessary to establish a suitable clearance of the slits of the partition diaphragm. Then it is preferable to appropriately regulate the rate of flow from the partition diaphragm to the secondary grinding chamber. It is to be noted that even though a rate of flow is once adequately balanced and the grinding operation takes place efficiently for a certain period based upon such predetermined balance, it is often the case that grindability and grain size distribution of cement clinker ground by the ball mill is not always constant but variable. It is, therefore, required to regulate the rate of flow from time to time following the variation.
To meet the mentioned requirement, Japanese Laid-Open Utility Model publication (unexamined) No.1-174047 proposed a construction as shown in FIGS. 6 (A) and 6(B), in which a screen plate 11b of the primary grinding chamber side is disposed on the front face of a partition diaphragm 1b and a screen plate 12b of the secondary grinding chamber is disposed on the rear face thereof to form a diaphragm chamber 14b in a space between the two screen plates. The circumference of the partition diaphragm is divided radially from a center core 2b into several divisions, and in each of the divisions a disc controller 4b is provided through the diaphragm chamber 14b from the outer shell 3b toward the center. A control disc 6b is mounted on one end of the disc controller 4b to open and close a discharge opening 17b provided surrounding the center core 2b by engaging and disengaging with a control disc seat 9 adjacent the discharge opening 17b. The disc controller 4b is supported by a support 10 in the diaphragm chamber and secured by driving a screw through the outer shell 3b of the mill on the outer periphery thereof. Accordingly, when driving the screw, the control disc 6b moves separating itself from the control disc seat 9, thereby all material in the diaphram chamber moves into the secondary grinding chamber. In this manner, the rate of flow passing through the diaphram chamber can be regulated by adjusting the relative position between the disc controller 4b and the control disc seat 9.
As is well known, a ball mill for grinding cement clinker is a rotating apparatus having a huge cylinder, the diameter of which amounts to 5.2 m with a length of up to 16.0 m (in case of the largest one) and in which a heavy weight ball is inserted and material to be ground is supplied. Moreover, the internal part of the ball mill is heated to high temperatures due to the heat generated by frictional grinding of the material. Also strong impact and vibration are directly applied to the body of the mill. Thus, it may be said that a ball mill is forced to perform operations under very severe conditions.
As a result, it is certain that a position of the disc controller with respect to the control disc seat can be adjusted in the early stage by loosening the screw with a tool such as a spanner from the outer shell of the mill thereby moving the disc controller forward or backward, but with the lapse of operating time the outer shell itself of the cylinder becomes deformed losing its circularity and, moreover, distortion between the control disc 6 and disc controller 4 occurs, and deformation and twisting of the disc controller itself are unavoidable. Thus, there is a possibility that the support 10 which has exactly supported the disc controller in the early stage of the grinding operation now acts to obstruct the forward or backward movement of the disc controller. In other words, there still remain several constructional disadvantages to be solved in the mentioned prior art in the sense of not being sufficiently resistant and endurable to the mentioned severe conditions peculiar to a huge apparatus such as a ball mill.